Hypothyroidism Glossary

Terms to know about the most common thyroid disorder

Animal (Desiccated) Thyroid Extract
A crude preparation made of animal, usually pig, thyroid glands. It was the first available source of thyroid hormone (thyroxine). It is still available today, but synthetic thyroid supplements are the preferred hypothyroid treatment.

Antibodies
Proteins produced by your body's immune system that attack invaders, such as a viruses. However, antibodies may also mistakenly attack healthy tissue. When antibodies attack the thyroid, it can stunt thyroid hormone production. This may result in hypothyroidism.

Anti-thyroid Drugs
Medications that slow down the thyroid gland's ability to produce thyroid hormone. By decreasing thyroid hormone production (this is the purpose when you're trying to treat an overly active thyroid), these medications increase your risk for hypothyroidism. There are several different types, but most interfere with the thyroid's ability to synthesize hormone.

Anti-thyroid Microsomal Antibodies Test
A third hypothyroid test is for anti-thyroid microsomal antibodies. These antibodies may attack thyroid cells. These antibodies can be classified as anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin (anti-Tg) antibodies. Their presence suggests underlying autoimmune destruction of the thyroid gland. Note: not everyone with autoimmune hypothyroidism has positive anti-thyroid antibodies. About 10-15% will be "antibody-negative" but still have autoimmune thyroid destruction.

Autoimmune Disease
A disease caused by a defect in the body's immune system. Instead of protecting the body, it attacks and destroys a healthy part of the body. Having an autoimmune disease is considered a risk factor for hypothyroidism.

Free T4 Test
A measure of the level of free T4 in your bloodstream. This test is a complimentary test to the TSH test. If your free T4 levels are too low, it's a strong indicator that you have hypothyroidism.

Goiter
Enlargement of the thyroid gland. When your thyroid is bombarded by signals from the pituitary in an effort to trigger the thyroid into making more hormones, the excessive stimulation may cause the thyroid gland to enlarge to the point where you have a bulge in your neck.

Hashimoto's Thyroiditis
Inflammation of the thyroid gland described by Dr. Hashimoto. It is the most common cause of hypothyroidism.

Hypothyroidism
An underactive thyroid gland—when the thyroid does not produce sufficient amounts of hormones. Symptoms are associated with decreased metabolism due to too little thyroid hormone in the blood.

Iodine
A non-metallic element found in food that is essential for normal thyroid function. The thyroid extracts iodine from the blood and incorporates it into thyroid hormone, which in turn, controls metabolism.

Levo-T
A brand of synthetic T4 hormone used to treat hypothyroidism.

Levothyroxine See synthetic thyroid supplements.

Levothyroxine Sodium
The generic name for synthetic T4 hormone used to treat hypothyroidism.

Levoxyl
A brand of synthetic T4 hormone used to treat hypothyroidism.

Metabolism
The body's ability to break down calories and oxygen to convert it to energy. The thyroid regulates metabolism.

Novothyrox
A brand of synthetic T4 hormone used to treat hypothyroidism.

Pituitary Gland
A small gland the size of a peanut that is located behind the eyes at the base of the brain. It secretes thyroid stimulating hormone (TSH), which helps control thyroid function.

Synthetic Thyroid Supplements Generally called levothyroxine, synthetic thyroid supplements are the standard treatment for hypothyroidism. They are man-made but are exactly the same as the T4 that is produced and released by the thyroid.

Synthroid
The most prescribed brand of synthetic T4 hormone used to treat hypothyroidism.

Thyroid Gland
Endocrine gland located in the neck that produces hormones to regulate metabolism. The thyroid gland is controlled by the pituitary gland, which secretes TSH in an effort to trigger thyroid hormone production. But sometimes the thyroid simply won't release enough hormones. An underactive thyroid gland—one that doesn't produce enough hormones—will results in hypothyroidism.

Thyroid Hormone Replacement Therapy
The basic concept of hypothyroid treatment includes ingesting daily hormones to compensate for the underactive thyroid. It usually includes a synthetic form of T4 hormone, but may combine T4 and T3 or be animal-derived.

Thyroid Stimulating Hormone (TSH)
A hormone produced by the pituitary gland that stimulates the thyroid gland to inhibit or release hormones.

Thyroiditis
Inflammation of the thyroid gland. This can affect the thyroid's ability to produce and secrete hormones and can lead to permanent destruction of the thyroid gland.

Thyroxine (T4)
The primary hormone produced and secreted by the thyroid gland. In treating hypothyroidism, man-made forms of T4 are the standard method. Along with T3, T4 controls your body's metabolism. If you don't have enough of them, then your metabolism slows down. In essence, T3 and T4 are in charge of how your body uses energy.

Triiodothyronine (T3)
The second hormone produced by the thyroid gland. It is more active than thyroxine (T4), but most medications from hypothyroidism do not include T3 hormone (your body can make T3 from T4, and taking T4 alone is usually sufficient to achieve normal thyroid function. Along with T4, T3 controls your body's metabolism. If you don't have enough of them, then your metabolism slows down. In essence, T3 and T4 are in charge of how your body uses energy.

TSH Test
The first line of testing for hypothyroidism. Your doctor will measure your thyroid stimulating hormone (TSH) levels with a blood test. TSH is secreted by the pituitary gland to stimulate thyroid hormone production. If TSH levels are too high, you will likely be diagnosed with hypothyroidism.

UNITHROID
A brand of synthetic T4 hormone used to treat hypothyroidism.

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